Last edit: 26/07/2013 Kernel event subsystem may be useful when writing drivers and kernel space services. It is not related to the subsystem of GUI events. An event, from the kernel's point of view, is a kernel space object which is owned by the thread that created it. struc EVENT { .magic dd ? ; 'EVNT' .destroy dd ? ; internal destructor .fd dd ? ; next object in list .bk dd ? ; prev object in list .pid dd ? ; owner (thread) id .id dd ? ; event uid. (just a number) .state dd ? ; internal flags; see below .code dd ? ; MSB: event class; next byte: priority ; (used by kernel only, always 0 for reading), ; The higher dword value the higher event priority. ; Two LSBs: event code. rd 5 ; .data: the structure of this field is not defined and ; depends on .code field. (Pass any data you need here) .size = $ - .magic .codesize = $ - .code } Realtime events have class 0хFF. Currently defined: EVENT.code= ; (Used in sound subsystem) RT_INP_EMPTY = 0xFF000001 RT_OUT_EMPTY = 0xFF000002 RT_INP_FULL = 0xFF000003 RT_OUT_FULL = 0xFF000004 Flags of EVENT.state field are defined in gui/event.inc. EVENT_SIGNALED = 0x20000000 ; bit 29: event is active/inactive EVENT_WATCHED = 0x10000000 ; bit 28: owner thread is waiting for the ; event to be active MANUAL_RESET = 0x40000000 ; bit 30: do not deactivate event : automatically on receive MANUAL_DESTROY = 0x80000000 ; bit 31: do not return event to a list of ; free ones on receive As of SVN r3732 (assume same below) the definition is located in /kernel/trunk/const.inc and is as follows: struct APPOBJ ; common object header magic dd ? ; destroy dd ? ; internal destructor fd dd ? ; next object in list bk dd ? ; prev object in list pid dd ? ; owner id ends struct EVENT APPOBJ id dd ? ; event uid state dd ? ; internal flags code dd ? rd 5 ; .data ends Code is located in gui/event.inc. Event objects live in kernel memory as a double-linked list (see fields .bk and .fd). While initialization the kernel reserves memory, creates 512 events and places them into FreeEvents list. When out of free event, kernel creates another 512 ones etc. Each thread has own double-linked lists where an event may be placed to: ObjList -- a list of kernel objects associated with the thread; EventList -- a list of kernel events for the thread. When events are moved between lists or reordered their data are not copied. This is done only via modification of .fd and .bk fields. These lists work as FIFO queues. Sending does not block, receiving blocks. Addressing is direct, by thread id. There always is an owner thread for an event. Event's life cycle is defined by flags while creation. By default the kernel uses values MANUAL_RESET = 0 and MANUAL_DESTROY = 0. Such an event is oneshot and is automatically freed by the kernel and returned to the FreeEvents list when received. An event with flag MANUAL_DESTROY = 1 becomes inactive when received but remains in thread's object list and can be reused. An event with flags MANUAL_DESTROY = 1 and MANUAL_RESET = 1 remains active when received and can be reset via call to ClearEvent. A life cycle example of a sound subsystem event: * For an audio buffer (possibly several) the driver creates an event in ObjList by calling CreateEvent with flag MANUAL_DESTROY. * Then driver calls WaitEvent for the event (waits for EVENT_SIGNALED event flag) and blocks waiting for buffer update request. * The buffer update request is sent with RaiseEvent from another thread. * Sending (RaiseEvent) and receiving (WaitEvent) are repeated as buffer gets empty. * Driver deactivates the event with ClearEvent when playback is stopped. Actually, the event structure is described here only for understanding of subsystem work principles. Direct field access is discouraged due to possible compatibility issues in the future. Only API calls should be used. A pair "pointer to an event" and "event id" is considered a single 64-bit id. This id should be stored somewhere after a call to CreateEvent for further work with the event. The kernel exports following event related functions: (for drivers, etc; called from kernel mode) CreateEvent RaiseEvent ClearEvent SendEvent DestroyEvent WaitEvent WaitEventTimeout GetEvent For user applications sysfn 68.14 (a wrapper to GetEvent) -------------------------------------------------------------------------------- CreateEvent: Creates a new event in ObjList queue of current thread. Sets: EVENT.destroy <= default internal destructor EVENT.pid <= current Process id EVENT.id <= unique id EVENT.state <= ecx: flags EVENT.code <= [esi]: size is 6*dword, do not copy if esi=0 Returns: eax -- pointer to the event or 0 for error. edx -- Event.id. Destroys: eax,ebx,edx,ecx,esi,edi -------------------------------------------------------------------------------- RaiseEvent: Activates existing event (may be owned by another thread) by setting EVENT_SIGNALED flag. Sets EVENT.code data if necessary. Does nothing more if EVENT_SIGNALED flag is already active in the event. If EVENT_SIGNALED flag is not set in the event it will be set, except when EVENT_WATCHED in edx = 1 and EVENT_WATCHED in the event = 0. I.e. while setting EVENT_WATCHED in edx it is checked if owner thread is waiting for event activation. No flags, except EVENT_SIGNALED, are modified in the event. Gets: eax -- pointer to event ebx -- id edx -- flags (see EVENT.state) Sets: EVENT.code <= [esi]: size is 6*dword, do not copy if esi=0 Returns: ? Destroys: eax,ebx,edx,ecx,esi,edi -------------------------------------------------------------------------------- ClearEvent: Move event to ObjList of owner thread. (May be it was already there.) Reset flags EVENT_SIGNALED and EVENT_WATCHED, keep other fields (.code, .id). Gets: eax -- pointer to event ebx -- id Returns: ? Destroys: eax,ebx,ecx,edi -------------------------------------------------------------------------------- SendEvent: Create a new event in the event list of target thread. Sets EVENT_SIGNALED flag in the event. Gets: EVENT.pid <= eax: target thread id; EVENT.code <= [esi]: size is 6*dword, do not copy if esi=0 Returns: eax -- pointer to event or 0 for error edx -- Event.id Destroys: eax,ebx,ecx,esi,edi -------------------------------------------------------------------------------- DestroyEvent: Moves event to FreeEvents, clears fields .magic, .destroy, .pid, .id. The event may be owned by other thread. Gets: eax -- pointer to event ebx -- event id Returns: eax -- 0 for error, non-zero for success Destroy: eax,ebx,ecx -------------------------------------------------------------------------------- WaitEvent: Wait infinitely until flag EVENT_SIGNALED is set in the event owned by the caller thread. This flag is set by signaling thread via RaiseEvent. Waiting thread is frozen by setting APPDATA.state <= TSTATE_WAITING=5. Flag EVENT_WATCHED is set in the event before freeze. If flag MANUAL_RESET is NOT set in the event then: EVENT_SIGNALED and EVENT_WATCHED are reset when the event is received. When MANUAL_DESTROY is inactive: the event is destroyed by DestroyEvent, active: the event is moved to ObjList of current thread. Gets: eax -- pointer to event ebx -- event id Returns: ? Destroys: eax,ebx,edx,ecx,esi,edi -------------------------------------------------------------------------------- WaitEventTimeout: Wait with a timeout until flag EVENT_SIGNALED is set in the event owned by caller thread. This flag is set by signaling thread via RaiseEvent. Waiting thread is frozen by setting APPDATA.state <= TSTATE_WAITING=5. Flag EVENT_WATCHED is set in the event before freeze. If flag MANUAL_RESET is NOT set in the event then: EVENT_SIGNALED and EVENT_WATCHED are reset when the event is received. When MANUAL_DESTROY is inactive: the event is destroyed by DestroyEvent, active: the event is moved to ObjList of current thread. Gets: eax -- pointer to event ebx -- event id ecx -- timeout, in ticks of system timer Returns: eax -- 0 if the event was not activated, or not 0 if activated Destroys: eax,ebx,edx,ecx,esi,edi -------------------------------------------------------------------------------- GetEvent: Waits infinitely for any event in the queue of current thread. Thread is frozen by setting APPDATA.state <= TSTATE_WAITING = 5. Event data (EVENT.code + 5*dword) are copied to specified buffer when received. Reset priority byte (see above) in the buffer. If flag MANUAL_RESET is NOT set in the event then: EVENT_SIGNALED and EVENT_WATCHED are reset when the event is received. When MANUAL_DESTROY is inactive: the event is destroyed by DestroyEvent, active: the event is moved to ObjList of current thread. Gets: edi -- pointer to buffer to copy data Returns: buffer with following data: +0: (EVENT.code) dword: id of following signal data +4: (EVENT.data) 5*dword: signal data, format depends on EVENT.code Destroys: eax,ebx,edx,ecx,esi,edi -------------------------------------------------------------------------------- SysFn 68.14 for application: ; wrapped GetEvent Waits infinitely for any event in the queue of current thread. Thread is frozen by setting APPDATA.state <= TSTATE_WAITING = 5. Event data (EVENT.code + 5*dword) are copied to specified buffer when received. Reset priority byte (see above) in the buffer. Gets: eax -- 68: function number ebx -- 14: subfunction number ecx -- pointer to data buffer (size is 6*dword) Returns: ecx = buffer with following data: +0: (EVENT.code) dword: id of following signal data +4: (EVENT.data) 5*dword: signal data, format depends on EVENT.code Destroys: eax